Lunar Rocks Lunar Interior Lunar Structure Lunar Formation Lunar Chronology Lunar Geology Lunar Exploration

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  • Lunar RocksLunar InteriorLunar StructureLunar FormationLunar ChronologyLunar GeologyLunar Exploration

  • Lunar Rocks

  • Lunar RocksBasic classification Elements - individual atom species that are the basic building blocks of ordinary matter

    Minerals - are composed of elements or compounds of the elements, and are often designated by the most common atoms/molecules contained in that mineral

    Rocks - composed of combinations of minerals/elements and can be classified into three major types on Earth: sedimentary, metamorphic and igneous

  • Lunar RocksBecause the Moon is small and there is no atmosphere, water is missing from the compounds that make up lunar rocks

    Sedimentary rocks are also not found on the Moon because there is no water or wind There are similarities in the lunar rocks and those found on Earth, including metal oxides, silicates, as well as some carbonaceous rocks

    The lack of pure metal oxides on the lunar surface which has no atmosphere does not exclude metal oxides that can be formed by the accretion of the planetesimal building blocks, and from igneous activity

  • Lunar RocksLunar rock samples

    During the Apollo program, 382 kg (842 lb) of Moon rock and "soil" was returned to Earth with most of the material composed of igneous rock, meaning it originates from the molten interior

    More recent measurements of the Moon's surface near the southern polar region that came from Clementine, Lunar Prospector, LCROSS, and Lunar Reconnaissance Orbiter spacecraft indicate ice deposits on or just under the lunar surface The wide variety of minerals and elements in the Apollo rock samples contained can be simplified into three rock types: basalt, breccia, and anorthocite

  • Lunar RocksBasalt

    Basaltic lava, or basalt, like the volcanic lava on Earth, is rich in olivine and pyroxene, and several elements which enhance the dark color of the rock, including titanium

    Basalt forms when magma flows onto the surface of the Moon, cools and then crystallizes

    Basalt lava flows are the dark materials that have filled the lowlands on the Moon's surface which cover about one-quarter the Moon's surface area

    The basalt flows are generally 3.1 to 3.8 billion years (Gigayears, or Gy) old

  • Lunar RocksBreccia

    Also found on Earth but in a different formation process, breccia rock is made of fragments of other rocks fractured and/or fused by collisions of meteoroids with the Moon

    Fragments heated by the collisions that broke them apart melted and stuck to other grains composed of broken rocks and smaller mineral grains

    Most breccias were produced when the original crust of the Moon was completely broken up by meteoroid impacts in its early history

  • Lunar RocksAnorthocite

    Anorthosite, also found in abundance on Earth, is a light-colored rock composed mostly of crystals of the mineral feldspar - primarily silicates

    Anorthosite rocks make up much of the highlands of the Moon, with the feldspars producing the light color

    The first feldspar crystals were pale gray or colorless and later broken into fragments; the resulting shattered feldspar crystals produced the whitish color

    Anorthosite represent the oldest formations on the Moon and are generally 4.0 to 4.3 Gy oldThe "Genesis Rock" brought back by the Apollo 15 astronauts, for example, was one of the oldest samples at 4.6 Gy

  • Lunar Structure

  • Lunar StatsMass7.349x1022 kg (1/81 MEarth)Radius 1,738 km (equatorial) (0.27 REarth)Mean density 3.35 g/cm3Orbital eccentricity 0.055Orbit inclination 5.14o (from Earth's equator)Semimajor axis 384,400 kmOrbit period 29.5 days solar (27.3 days sidereal)Rotation period 29.5 daysMagnetic field
  • Lunar InteriorThe Moon's 1,734 km radius spans an iron core approximately300 - 425 km thick, a mantle approximately 1,000 km wide, and a relatively thick crust that ranges from tens of km to 100 km deep, with an average of 45 km

    Estimates of the lunar interior are primarily based on seismic data collected during and after the Apollo missions, and satellite data from various lunar orbiter missions

    Seismic wave propagation and wave refraction were also used to constrain density, pressure values of the interior, as well as the most likely chemistry located at/near the discontinuities between the three layers

  • Lunar Highlands The Moon's early molten mantle that is often referred to as the "magmatic ocean began cooling and separating with lighter-weight plagioclase rising to the surface to shape the lunar crust

    The Moon's original plagioclase crust identified as highlands because of its generally higher elevation experienced an intrusion of slightly heavier magnesium-rich magma that contained less plagioclase and more olivene and pyroxene

  • Lunar Highlands These later intrusions were also richer in potassium (K), phosphorous (P), and rare-earth elements (REE), and as such are identified by the acronym KREEP

    Crust formation ended 4.1 billion years ago when the upper-mantle solidified

    These later formations constitute about of the highland regions, yet provide insight into the formation and early evolutionary processes of the Moon

  • Lunar Maria Heavy bombardment of the lunar surface continued until approximately 3.9 billion years ago

    The violent impacts not only cratered the lunar surface permanently, but created a layer of rubble, growing deeper and more fragmented with time lunar regolith

    As planetesimal impacts began to wane, the insulation properties of the thickening crust and continuing radioactivity decay began heating the interior

  • Lunar Maria At approximately 3.9 billion years, the fractured, cratered, and thinning crust, although less dense than the mantle, placed enormous pressure on the molten magma below, forcing it to flow through the fissures into the lower basins of the largest and deepest craters

    The darker, denser magma (containing dark colored olivene and pyroxene) cooled after filling the lowest regions, forming large regions outlined by the largest, oldest, deepest crater basins

    These vast areas called maria, or seas, have distinctly different geological appearance and composition

  • Lunar Maria The most distinctive difference is the dark, smooth surface of the mare compared to the rough highlands

    Because the impacts declined in size and number, the younger lunar mare show fewer large craters than the highlands

  • Lunar Formation

  • Lunar Surface Composition Anorthocite, which is predominantly aluminum-calcium silicates, offers a greater abundance of both calcium and aluminum than in the Earth's crust

    These two important elements can be employed in lunar outpost construction and manufacturingA variety of other materials and elements can be produced from anorthocite, including silica glass (silicon oxides), pure silicon, calcium oxide (lime), and alumina (aluminum oxide)

    Basalt is composed of a broad combination of silicate and oxide minerals that are rich in magnesium, iron and titanium

    These minerals are commonly metal oxides (MgO, TiO, FeO), combined with silica

  • Lunar Surface Composition One of the more common metal oxide silica minerals in the lunar basalts is olivene, which is a combination of magnesium oxide plus silica

    A very important and abundant lunar surface mineral is ilmenite (FeTiO3) that is important because of its oxygen content Useful as a propellant and for breathingTitanium content can be used for high-temperature and light-weight structural metal

  • Lunar Magnetic Field The lack of a significant magnetic field on the Moon suggests a solid or nearly solid core if one assumes a traditional geodynamic magnetic field

    The magnetized surface rock indicates a very small but measurable lunar magnetic field at various times during the crustal rock formation

    Slight magnetization also appears in the highlands, possibly due to impact shock

    Previously magnetized rock helps establish the time of crustal formation and the approximate period of the core's dynamical motion

  • Lunar Formation Lunar formation constraints on physical models (theories)

    Ratios of oxygen isotopes (O16/O17/O18) in the Earth and the Moon are the sameThe Moon and the Earth have differences in various other isotopic ratiosThe Earth's density is 5.5 g/cm3 and the Moon's is 3.3 g/cm3The Moon crust is ~12% iron while the Earths is ~4%The mantles of the Earth and the Moon have distinctly different iron/nickel/cobalt metal (siderophile) signaturesRefractory (high-temperature) element concentrations are higher in the Moon than in the Earth, however, their ratios are the sameAngular momentum of the Earth-Moon system is higher than any known planet-satellite system

  • The Four Basic Theories of Lunar Formation

    1. Capture2. Coaccretion3. Fission4. Collision

  • Lunar Formation 1. Lunar capture The Earth and Moon would both be in heliocentric orbits with a gravitational capture of the Moon by the Earth as the Moon passed by (but needs something to remove binding energy)

    Attractive because of its simplicity

    Easily dismissed because of the different composition abundance of Earth and Moon (especially iron) Also has difficulty because of the binding energy would be much smaller than observed

  • Lunar Formation 2. Coaccretion As the Earth accumulates (accretes) planetesimal material from bombardment in its early formation, it is possible that a smaller body could be created in the same region from the same material

    Attractive because of simplicity and the lack of a unique, catastrophic event

    Highly improbable because the actual composition